1. Field of the Invention
The present invention relates to an intermediate hopper and an image forming apparatus. More particularly, the present invention relates to an intermediate hopper for temporarily containing toner to be supplied to a developing device and an image forming apparatus such as an electrostatic copying machine, a laser printer and a facsimile machine that forms images by an electrophotographic method by guiding the toner contained in the intermediate hopper to the developing device.
2. Description of the Related Art
In the image forming apparatus using the electrophotographic method, an electrostatic latent image is formed on a surface of a photoconductor drum (toner image holder), toner is supplied to the photoconductor drum by means of a developing device to develop the electrostatic latent image, a toner image formed on the photoconductor drum through the development is transferred onto a sheet such as a paper sheet, and the toner image is fixed onto the sheet by means of a fixing device.
Since the toner is consumed at every image formation, the developing device is replenished with toner stored in a toner cartridge. Nowadays, there is an image forming apparatus available which employs an intermediate hopper for temporarily containing toner instead of supplying the toner directly from a toner cartridge to a developing device.
In this image forming apparatus, the toner stored in the toner cartridge is supplied to the intermediate hopper, and the toner supplied to the intermediate hopper is supplied to the developing device.
With such an intermediate hopper, even when the toner in the cartridge runs out, it is possible to secure the time needed to remove the empty toner cartridge and replace it with a new toner cartridge without suspending a printing operation in the image forming apparatus, because the intermediate hopper contains the toner.
That is, with the intermediate hopper, it is possible to continue an image formation operation during the replacement of the toner cartridge (referred to as continuous run).
For example, Japanese Unexamined Patent Application Publication No. 2009-251169 proposes an intermediate toner hopper comprising: a container tank for temporarily containing toner discharged from a toner bottle; and two carrying screws arranged in the container tank so that axis lines thereof are parallel to each other for carrying the toner in opposite directions by rotating in opposite directions, wherein the toner discharged from the toner bottle is received through a toner supply opening formed in the container tank and temporarily contained, guided toward a toner discharge opening formed in the container tank while being circulated and carried by the rotation of the two carrying screws, and then discharged into a developing device through the toner discharge opening (see FIGS. 1 and 4, and paragraphs 0056 to 0067).
While being able to discharge some of the toner being circulated and carried inside the container tank swiftly by using the two carrying screws, the above-described intermediate toner hopper is disadvantageous in that the toner stays at an end of the container tank because the two carrying screws do not have a partition therebetween and in that the toner is deteriorated due to continuous and prolonged agitation by the two carrying screws.
The staying of the toner may be prevented by providing a partition between the two carrying screws, and circulating and carrying the toner along toner carrying paths having each carrying screw.
The staying of the toner can be prevented, because the toner can be discharged bit by bit through the toner discharge opening while being circulated and carried, so that the toner supplied through the toner supply opening first is discharged first.
However, when the supply of the toner from the toner bottle is suspended for replacement of the toner bottle in the case with the partition for circulating and carrying the toner, the toner carrying paths will have a region having no toner or a region having a low toner density (hereinafter, referred to as toner-missing space).
The toner-missing space is also carried toward the toner discharge opening with the toner carried by the carrying screws. When the toner-missing space reaches the toner discharge opening, the supply of the toner to the developing device is suspended to reduce the toner density in the developing device. The toner thus supplied unsteadily and nonuniformly may cause an uneven image.